If you already hold a cobranded card then getting a core card that too LTF might not be a cake walk irrespective of the limit on existing card. We have plenty of other peoples experience who have cited this as an issue and were left with no other option than to close existing co Branded card, wait out the cooling period and then apply.
@ltf4ever did you also meet the income criteria? I have a credit limit greater than 5L but don't meet the income eligibility criteria. Can I get the DCB C2C?